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Knob-and-tube wiring in insulation

Now I am back to the issue of dense-packed cellulose in a house where knob and tube is in most of the exterior walls. I see lots of older homes installing cellulose and or fiberglass blown into the walls....just as an energy upgrade not as a whole house redo (gutted and re-wired etc.)

What are the electrical codes saying with regard to knob and tube exposure to insulation that is blown in... is this safe?


Asked by susan clellen
Posted Jun 8, 2011 8:31 AM ET
Edited Jun 8, 2011 8:26 PM ET


6 Answers

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NEC 2011 Article 394 Concealed Knob-and-Tube Wiring
394.12 Uses Not Permitted
(5) Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed-in-place insulating material that envelops the conductors.

The problem is that the average insulation installer does not know or does not care about electrical codes. Combine insulation with wiring protected with breakers larger than originally intended is a disaster waiting to happen.

Answered by Nathan Spriegel
Posted Jun 8, 2011 8:50 AM ET
Edited Jun 8, 2011 10:07 AM ET.


Thanks Nathan. I am so done with industrial methods and materials...Each generation comes out with the next best thing since burnt toast ! Plan C is to apply 2 " of light straw/cob and earth-plaster over the old plaster walls and be done.


Answered by susan clellen
Posted Jun 8, 2011 12:32 PM ET


I would take this as a chance to perform an electrical evaluation and determine if electrical upgrades should be performed anyway. Most houses with knob and tube do not have enough circuits to serve modern requirements My own house only had three circuits to serve all general-use receptacles, including the two bedrooms. That is why people often replace the 15 amp fuse/breaker with 20 amp ones. Added benefits would include proper grounding-type receptacles and AFCI protection.

Answered by Nathan Spriegel
Posted Jun 8, 2011 2:04 PM ET
Edited Jun 8, 2011 2:29 PM ET.


You should probably read this before going any further with your renovation:

Answered by James Morgan
Posted Jun 8, 2011 3:02 PM ET


Knob and tube should really be replaced whenever feasible.

Answered by Eric Dymond
Posted Jun 8, 2011 4:10 PM ET


I've spoken to a lot of weatherization workers and cellulose installers over the years, and fortunately they all know the rule -- you can't install cellulose over knob-and-tube wiring. Insulation upgrades are a good opportunity to perform wiring upgrades.

Answered by Martin Holladay
Posted Jun 8, 2011 8:28 PM ET

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